The present invention is directed to methods for analyzing chemical samples automatically with minimum manual involvement. Generally the less manual involvement, the less danger from toxic chemicals and the lower the cost of the analysis. The present invention is also directed to apparatus and method for improved sensitivity in obtaining information about chemical samples.
One type of automated analysis of a chemical sample is an "excitation" technique where the sample is subjected to an excitation input signal. Different compounds in the sample produce different output signals. The output signals are analyzed to identify or quantify the compounds in the sample emitting the output signals.
One method of analyzing an output signal is by comparing its wavelength with the wavelength of the excitation input signal generating the output signal. The output signal can include "non-resonant" and "resonant" signals. Where the wavelength of the output signal is substantially dependent on the wavelength of the input signal, the output signal is termed a "non-resonant" signal. Examples of such non-resonant signals are Rayleigh signals, Mie scattering, Brillouin scattering and/or Raman scattering. Where the wavelength of the output signal is substantially independent of the wavelength of the input signal, the output signal is termed a "resonant" signal. Examples of such resonant signals are fluorescence and phosphorescence signals. A problem with existing excitation technique is that the resonant and non-resonant signals interfere with each other and can overlap in frequency. Therefore, it is not easily possible to distinguish between the resonant and non-resonant signals.
Another problem with the excitation technique results from scattering of the input signals. Such scattering can result from scattering of off-fundamental input signals and by inelastic scattering, for example, Raman scattering of water.
Therefore, there is a need for a method and apparatus to accurately determine the analyte content of a sample wherein the sample, when activated by an input signal, generates a resonant and a non-resonant signal.